1 files changed, 219 insertions, 0 deletions
diff --git a/lib/libc/string/strstr.c b/lib/libc/string/strstr.c
new file mode 100644
index 000000000000..90f8bc701e0f
--- /dev/null
+++ b/lib/libc/string/strstr.c
@@ -0,0 +1,219 @@
+/*-
+ * SPDX-License-Identifier: MIT
+ *
+ * Copyright (c) 2005-2014 Rich Felker, et al.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+ * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+ * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+ * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+ * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+#include <stdint.h>
+#include <string.h>
+
+static char *
+twobyte_strstr(const unsigned char *h, const unsigned char *n)
+{
+	uint16_t nw = n[0] << 8 | n[1], hw = h[0] << 8 | h[1];
+	for (h++; *h && hw != nw; hw = hw << 8 | *++h)
+		;
+	return *h ? (char *)h - 1 : 0;
+}
+
+static char *
+threebyte_strstr(const unsigned char *h, const unsigned char *n)
+{
+	uint32_t nw = (uint32_t)n[0] << 24 | n[1] << 16 | n[2] << 8;
+	uint32_t hw = (uint32_t)h[0] << 24 | h[1] << 16 | h[2] << 8;
+	for (h += 2; *h && hw != nw; hw = (hw | *++h) << 8)
+		;
+	return *h ? (char *)h - 2 : 0;
+}
+
+static char *
+fourbyte_strstr(const unsigned char *h, const unsigned char *n)
+{
+	uint32_t nw = (uint32_t)n[0] << 24 | n[1] << 16 | n[2] << 8 | n[3];
+	uint32_t hw = (uint32_t)h[0] << 24 | h[1] << 16 | h[2] << 8 | h[3];
+	for (h += 3; *h && hw != nw; hw = hw << 8 | *++h)
+		;
+	return *h ? (char *)h - 3 : 0;
+}
+
+#define MAX(a, b) ((a) > (b) ? (a) : (b))
+#define MIN(a, b) ((a) < (b) ? (a) : (b))
+
+#define BITOP(a, b, op) \
+	((a)[(size_t)(b) / (8 * sizeof *(a))] op \
+	    (size_t)1 << ((size_t)(b) % (8 * sizeof *(a))))
+
+/*
+ * Two Way string search algorithm, with a bad shift table applied to the last
+ * byte of the window. A bit array marks which entries in the shift table are
+ * initialized to avoid fully initializing a 1kb/2kb table.
+ *
+ * Reference: CROCHEMORE M., PERRIN D., 1991, Two-way string-matching,
+ * Journal of the ACM 38(3):651-675
+ */
+static char *
+twoway_strstr(const unsigned char *h, const unsigned char *n)
+{
+	const unsigned char *z;
+	size_t l, ip, jp, k, p, ms, p0, mem, mem0;
+	size_t byteset[32 / sizeof(size_t)] = { 0 };
+	size_t shift[256];
+
+	/* Computing length of needle and fill shift table */
+	for (l = 0; n[l] && h[l]; l++)
+		BITOP(byteset, n[l], |=), shift[n[l]] = l + 1;
+	if (n[l])
+		return 0; /* hit the end of h */
+
+	/* Compute maximal suffix */
+	ip = -1;
+	jp = 0;
+	k = p = 1;
+	while (jp + k < l) {
+		if (n[ip + k] == n[jp + k]) {
+			if (k == p) {
+				jp += p;
+				k = 1;
+			} else
+				k++;
+		} else if (n[ip + k] > n[jp + k]) {
+			jp += k;
+			k = 1;
+			p = jp - ip;
+		} else {
+			ip = jp++;
+			k = p = 1;
+		}
+	}
+	ms = ip;
+	p0 = p;
+
+	/* And with the opposite comparison */
+	ip = -1;
+	jp = 0;
+	k = p = 1;
+	while (jp + k < l) {
+		if (n[ip + k] == n[jp + k]) {
+			if (k == p) {
+				jp += p;
+				k = 1;
+			} else
+				k++;
+		} else if (n[ip + k] < n[jp + k]) {
+			jp += k;
+			k = 1;
+			p = jp - ip;
+		} else {
+			ip = jp++;
+			k = p = 1;
+		}
+	}
+	if (ip + 1 > ms + 1)
+		ms = ip;
+	else
+		p = p0;
+
+	/* Periodic needle? */
+	if (memcmp(n, n + p, ms + 1)) {
+		mem0 = 0;
+		p = MAX(ms, l - ms - 1) + 1;
+	} else
+		mem0 = l - p;
+	mem = 0;
+
+	/* Initialize incremental end-of-haystack pointer */
+	z = h;
+
+	/* Search loop */
+	for (;;) {
+		/* Update incremental end-of-haystack pointer */
+		if (z - h < l) {
+			/* Fast estimate for MAX(l,63) */
+			size_t grow = l | 63;
+			const unsigned char *z2 = memchr(z, 0, grow);
+			if (z2) {
+				z = z2;
+				if (z - h < l)
+					return 0;
+			} else
+				z += grow;
+		}
+
+		/* Check last byte first; advance by shift on mismatch */
+		if (BITOP(byteset, h[l - 1], &)) {
+			k = l - shift[h[l - 1]];
+			if (k) {
+				if (k < mem)
+					k = mem;
+				h += k;
+				mem = 0;
+				continue;
+			}
+		} else {
+			h += l;
+			mem = 0;
+			continue;
+		}
+
+		/* Compare right half */
+		for (k = MAX(ms + 1, mem); n[k] && n[k] == h[k]; k++)
+			;
+		if (n[k]) {
+			h += k - ms;
+			mem = 0;
+			continue;
+		}
+		/* Compare left half */
+		for (k = ms + 1; k > mem && n[k - 1] == h[k - 1]; k--)
+			;
+		if (k <= mem)
+			return (char *)h;
+		h += p;
+		mem = mem0;
+	}
+}
+
+char *
+strstr(const char *h, const char *n)
+{
+	/* Return immediately on empty needle */
+	if (!n[0])
+		return (char *)h;
+
+	/* Use faster algorithms for short needles */
+	h = strchr(h, *n);
+	if (!h || !n[1])
+		return (char *)h;
+	if (!h[1])
+		return 0;
+	if (!n[2])
+		return twobyte_strstr((void *)h, (void *)n);
+	if (!h[2])
+		return 0;
+	if (!n[3])
+		return threebyte_strstr((void *)h, (void *)n);
+	if (!h[3])
+		return 0;
+	if (!n[4])
+		return fourbyte_strstr((void *)h, (void *)n);
+
+	return twoway_strstr((void *)h, (void *)n);
+}